Predicting Ambulatory Function Based on Infantile Lower Extremity Posture Types in Amyoplasia Arthrogryposis

BACKGROUND: Arthrogryposis multiplex congenita (AMC) is a nonprogressive syndrome with multiple rigid joints, fibrotic periarticular tissue, and muscular fibrosis. The most common subgroup is amyoplasia. Ambulation is one of the most significant functions of the lower extremities as it translates to increased functionality and independence in adulthood. There is no predicative scale to determine ambulation at maturity for the infant with amyoplasia. It is believed lower extremity resting position of infants with amyoplasia potentially correlates with ambulation at maturity. The purpose of this study was to classify the infantile position of lower extremities and muscle strength to predict ambulation potential at maturity. METHODS: Children with amyoplasia were retrospectively reviewed and classified into groups based on infantile position of hip-knee alignment and limb muscle function. Sitting, standing, and walking skills from infancy into adulthood were evaluated. The ambulation function was correlated with the infantile position of the lower extremities. RESULTS: Amyoplasia cases were sorted into 5 types and correlated with ambulatory potential. Type I: mild ambulatory impairment with infantile position of flexed knees and hips but full range of motion. At maturity, all were community ambulators. Type II: moderate ambulatory impairment having infantile position of hip flexion, hip external rotation, and knee flexion contractures. Hip abductors and external rotators had antigravity strength. All stood and walked during the first decade of life with knee ankle foot orthoses. Type III: severe ambulatory impairment having infantile position of hip flexion, abduction, external rotation, and knee flexion contractures but lacked hip muscle recruitment. All used wheelchairs at maturity. Type IV: mild ambulatory impairment with infantile position of extended knees and flexed dislocated hips. At maturity, 90% were community ambulators. Type V: variable ambulatory impairment having asymmetric hip and knee alignment with unilateral hip dysplasia with extended knee and opposite limb flexed. Ambulation skill varied at maturity with 27% full-time wheelchair users. CONCLUSIONS: Amyoplasia can be sorted by infantile position of lower extremities and muscle strength into 5 types to predict ambulatory function. LEVEL OF EVIDENCE: Level III-Prognostic Study.